JPH04131014U - Bias circuit for operational amplifiers - Google Patents

Abstract

(57) [Summary] [Purpose] The present invention relates to a bias circuit for an operational amplifier that biases an input signal to an operational amplifier that amplifies an analog signal, and its purpose is to prevent the generation of noise that occurs when power is turned on to the operational amplifier. [Structure] In order to supply a DC bias voltage to one input terminal of the operational amplifier (1), a first resistor (2) whose one end is connected to the input terminal and whose other end is grounded.
a second resistor (3), one of which is connected to the first resistor (2) and the other to a DC power supply, and a first resistor (3) connected in parallel to the first resistor (2). A second capacitor (5) connected in parallel to the second resistor (3) and having substantially the same capacitance as the first capacitor (4) is provided in the operational amplifier bias circuit having a capacitor.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention biases the input signal to an operational amplifier that amplifies analog signals. The present invention relates to a bias circuit for an operational amplifier. The purpose of this invention is to prevent the noise that occurs when power is turned on to the operational amplifier. do.

0002

[Conventional technology]

FIG. 5 is a diagram showing a conventional bias circuit for an operational amplifier. In addition, throughout the diagram Similar components are represented by the same reference numerals or symbols. The structure of this diagram is , an operational amplifier 1, one of which is connected to the non-inverting terminal of the operational amplifier 1 and whose a first resistor 2, the other of which is grounded, and one of which is connected to and connected to the first resistor 2; A second resistor 3, the other of which is connected to a DC voltage power supply, and a second resistor 3 connected in parallel to the first resistor 2. a first capacitor 4 connected to the circuit, one of which receives the signal and the other of which receives the signal; A resistor 6 is connected to the inverting input terminal of the amplifier 1, and one of the resistors is connected to the output terminal of the operational amplifier 1. The input voltage includes a feedback resistor 7, the other side of which is connected to its inverting input terminal.

0003 Here, the resistance values of the first resistor 2, second resistor 3, resistor 6, and resistor 7 are respectively set to R. ₁ ,R₂,R₃and R_Fourand the capacitance of the first capacitor 4 is C₁shall be. Next, the operation will be explained. FIG. 6 is a diagram showing signal waveforms at each part of the operational amplifier. Book Figure (a) shows a signal input to the resistor 6 at the inverting terminal of the operational amplifier 1. this The signal is an alternating current signal that is positive or negative with respect to the base line of 0V. This diagram (b) shows the bias circuit Assuming that the first and second resistors 2 and 3 are not present, the output of the operational amplifier 1 is Since operational amplifier 1 and resistors 6 and 7 constitute an inverting amplifier circuit, Its closed loop gain G is G=-R_Four/R₁become. This figure (c) shows the amplified intersection described above. A voltage V obtained by dividing the current signal by the first and second resistors_B=V_CC・R₁/(R₁+R₂) are shown superimposed to show the biased AC signal. Here V_CCis a DC voltage power supply be. The biased signal is then subjected to various processing and finally is played on the speaker.

0004

[Problem that the idea aims to solve]

However, the conventional bias circuit for an operational amplifier has a problem in that noise is generated when the power is turned on for the following reason. FIG. 7 is a diagram showing changes in bias voltage V _B when power is turned on. When the power is turned on, the first capacitor 4 is charged from the power supply via the second resistor 3 with a time constant R ₂ C ₁ , but at the same time, the first capacitor 4 is charged via the first resistor 2 with a time constant R ₁ C ₁ , a discharge occurs. Therefore, as shown in FIG. 7, it takes a long time T until the bias voltage reaches the predetermined value _VB . FIG. 8 is a diagram showing the output signal of the operational amplifier when the power is turned on. As shown in this figure, the bias voltage of the output signal of operational amplifier 1 is in a transient state for time T after the power is turned on, so it is not normally biased with respect to the input signal, so the subsequent signal processing during this period is normal. It is not processed and is formed as noise. On the other hand, if signal processing is stopped during this time, noise will not be generated, but another problem will arise in that the responsiveness will deteriorate.

[0005] Therefore, in view of the above-mentioned problems, the present invention is designed to easily prevent overloading of the bias voltage when the power is turned on. An object of the present invention is to provide an operational amplifier bias circuit that can prevent transient changes.

[0006]

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides a direct current bias to one input terminal of the operational amplifier. One of them is connected to the input terminal and the other is connected to supply the ground voltage. a first resistor connected to the ground, one of which is connected to the first resistor, and the other is connected to the DC a second resistor connected to a power supply; and a first capacitor connected in parallel to the first resistor. an operational amplifier bias circuit having a resistor connected in parallel to the second resistor; A second capacitor is provided that is substantially the same in capacity as the first capacitor.

[0007]

[Effect]

According to the operational amplifier bias circuit of the present invention, the capacitance of the first and second capacitors is the vias formed by the second capacitor by making the quantities substantially the same; The power-up transient of the bias voltage is caused by the bias voltage formed by the first capacitor. Since the voltage transient state is canceled out, the bias voltage rises immediately when the power is turned on, and the output The signal is no longer subject to DC voltage fluctuations.

[0008]

【Example】

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an operational amplifier bias circuit according to an embodiment of the present invention. The configuration in this figure is _different from that _shown in FIG. This is capacitor 5. FIG. 2 is a diagram showing the bias voltages generated by the first and second capacitors 4 and 5 when the power is turned on. The bias voltage generated by the first capacitor 4 in the figure is the one without the second capacitor 5, and is formed in the same manner as described in FIG. On the other hand, the bias voltage of the second capacitor 5 is the one without the first capacitor 4, and when the power is turned on, although it is not initially charged, the time constant R ₁ C is applied via the first capacitor 2. ₂ , and at the same time, it is discharged via the second resistor _R2 with a time constant _R2C2 . Therefore, after the time T has elapsed after the power _is turned on, a constant voltage determined by the first and second resistors 2 and 3 is discharged. The voltage becomes V _B.

FIG. 3 is a diagram showing the composition of the bias voltages in FIG. 2. As shown in this figure, by providing the second capacitor 5 for the first capacitor 4 and setting the respective capacitances to C ₁ ≒ C ₂ , the transient states of the respective bias voltages in FIG. 2 are canceled out, The composite bias rises immediately after the power is turned on, and becomes the bias voltage determined by the first and second resistors 2 and 3, so that no long-term transient state occurs as in the conventional case.

0010 FIG. 4 is a diagram showing the output signal of the operational amplifier when the power is turned on. As shown in this figure Since there is no longer a transient state in the bias voltage immediately after the power is turned on, the output of operational amplifier 1 Since the normal bias is also given to the force signal from the beginning, this signal and the subsequent processing circuit Even if the signal is sent out to the road, normal signal processing is performed instead of generating noise as in the case of conventional methods. . This prevents the occurrence of this problem when the power is turned on.

[0011] The above was explained as a bias circuit used in an operational amplifier, but a filter circuit The same can be said for etc.

0012

[Effect of the idea]

As explained above, according to the present invention, the voltage that is the bias circuit of the operational amplifier is Since capacitors with the same capacity are placed in parallel with each voltage dividing resistor, when the power is turned on, The bias voltage no longer has a transient state and becomes a constant bias voltage, preventing noise generation. Can be stopped.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an operational amplifier bias circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing bias voltages due to first and second capacitors when power is turned on.

FIG. 3 is a diagram showing a synthesis of bias voltages in FIG. 2;

FIG. 4 is a diagram showing the output signal of the operational amplifier when the power is turned on.

FIG. 5 is a diagram showing a conventional operational amplifier bias circuit.

FIG. 6 is a diagram showing signal waveforms of each part of the operational amplifier.

FIG. 7 is a diagram showing changes in bias voltage when power is turned on.

FIG. 8 is a diagram showing the output signal of the operational amplifier when the power is turned on.

[Explanation of symbols]

1...Operation amplifier 2, 3...Resistance 4, 5...Capacitor

Claims (1)

[Scope of utility model registration request] 1. A first resistor (2), one of which is connected to the input terminal and the other of which is grounded, in order to supply a DC bias voltage to one input terminal of the operational amplifier (1); a second resistor (3), one of which is connected to the first resistor (2) and the other connected to the DC power supply;
and a first capacitor connected in parallel to the first resistor (2),
A bias circuit for an operational amplifier, characterized in that it comprises a second capacitor (5) connected in parallel to the second resistor (3) and having substantially the same capacity as the first capacitor (4).